Handover procedures are well known in the art of cellular telephony. A mobile subscriber unit, i.e., a mobile station, typically connects to a cellular network by detecting some form of beacon signal transmitted by a Base Transceiver Station (“BTS”) and then synchronizing itself to that BTS. During a call, the mobile station and/or the network monitor criteria such as the Radio Signal Strength Indication (“RSSI”) at either the mobile station and/or a base station and decide when the mobile station should handover to another BTS. More sophisticated criteria related to voice quality are also often utilized for making handover decisions, for example Bit Error Rate (“BER”) or Frame Erasure Rate (“FER”).
Wireless networks that utilize cellular air interface technology and enable handover of a mobile station from a cellular network Mobile Switching Center (“MSC”) to a Private Branch Exchange (“PBX”) coverage area are known. Networks of this type can be employed as enterprise networks providing businesses with “on campus” coverage. For example, a Global System For Mobil Communications (“GSM”) mobile subscriber using a GSM cellular network, who is also an enterprise subscriber, may handover to an enterprise GSM network upon moving into a radio coverage area of the enterprise campus. The local PBX functionality is utilized for switching calls internal to the PBX network, or to a Public Switched Telephone Network (“PSTN”) for external calls, thus saving the enterprise the cost imposed by the external cellular network switching as known in the art.
Handover of a mobile station between a cellular network and an enterprise network incorporating the same radio interface technology is, in general, accomplished by coordinating the communication and control links with the mobile station, the cellular network, and the enterprise network. These known handover methods require the wireless network to employ the same radio interface technology as the cellular network, and also require the MSC and PBX to communicate, for example via SS7 messaging. Therefore, an enterprise user must subscribe to a particular cellular provider in order to use the same mobile station on both networks.
Existing enterprise networks need to coordinate with a cellular network, using a protocol such as SS7 messaging, in order to handover a mobile station between the enterprise and cellular networks. These requirements for coordinating with a cellular network place a significant burden upon the operator of an enterprise network. First, the air interface technology of the cellular operator limits the choice of mobile stations that the enterprise operator can utilize within the enterprise. Additionally, the coordination required between the two networks limits the enterprise to cellular operators that provide on-campus solutions with their respective service offerings.
There would be benefits to enterprise network operators and users if mobile stations could operate, in a seamless manner, between cellular and wireless networks independent from the cellular air interface and control coordination technology. An enterprise will benefit in higher productivity and cost savings where its users operate a single mobile station both on and off the enterprise campus. An individual user would benefit from a single personal device that could be used for multiple purposes, for example work related and personal communications. Enterprise users will also, in general, not employ the same cellular operators as each individual enterprise user employs for personal use. Businesses are generally constrained to select providers based upon cost. Other considerations such as feature availability and interoperability between the enterprise and external networks is also a consideration for businesses. The best of both worlds is difficult to achieve in these respects.
In addition, other modes of service enhancements, or service enhancement businesses could exist if there were a means of utilizing wireless networks independently from the cellular technology employed by the mobile station. It is the aspect of handover control by the cellular network that is a limiting factor in achieving such seamless mobility of a mobile station.
Therefore, a need exists for an apparatus and method for implementing bi-directional soft handovers between a cellular network and a wireless network without cellular network control intervention.